This invention relates generally to identity verification techniques using biometric data and, more specifically, to the use of biometric data, such as fingerprints, to provide identity verification in real time. Although techniques for biometric verification of personal identity have been widely disclosed, widespread application of biometric identity verification systems to consumers has not occurred, largely because of the relatively high cost and lack of practical usability of such systems for high-speed or real-time identity verification. To be usable in a practical application, a biometric verification system must meet requirements of accuracy, size and convenience. “Accuracy” pertains principally to the percentage of access requests that are granted to legitimate users on a first attempt. “Size” refers to the size of scanning and verification equipment, and particularly the size of the fingerprint scanner. As will be further discussed, the scanner size has an impact on cost, speed of operation, and convenience for the user. “Convenience” includes ease of use as well as speed of operation. A fingerprint scanner may be easy to use, but a long processing delay will reduce its overall convenience. Low accuracy also negatively impacts convenience of use.
Devices using fingerprint scanning of a single finger, with either rolled or flat scanning, have a single trial accuracy limit of 95–99% using any currently known fingerprint matching algorithm. Thus, between one and five of every one hundred attempts at identity verification by legitimate users will result in failure to gain access to whatever is being protected by the biometric device. Upon rejection, the user must make another attempt, possibly using an alternate finger if the system has been set up to accommodate this type of action. In many important applications of biometric verification, this level of accuracy is not acceptable from a convenience standpoint.
Although accuracy can be improved by increasing the size of the fingerprint scanner to accommodate a larger area of the finger, or possibly two fingers, there is an important tradeoff that designers of such systems face. Larger scanning devices cost significantly more and require a significantly longer processing time. In fact the cost of a fingerprint scanner increases at greater than a linear rate. That is to say, the cost of one large sensor will be significantly greater than the combined cost of two sensors of half the size of the large sensor. The processing time for virtually all verification algorithms is roughly proportional to the square of the sensor size. Accordingly, improvements in accuracy obtained by using a larger fingerprint sensor are accompanied by both a higher sensor cost and a longer processing time. In other words, accuracy is improved only at the expense of economy and convenience.
All commercially available fingerprint identity verification systems available at the time of the present invention utilize single finger collection and verification, with two possible exceptions. Both arise in law enforcement applications, where real-time identity verification is rarely a concern. Some police agencies use a single fingerprint capture device to capture images of all ten fingers in succession. The images are not captured simultaneously and the purpose is not to support real-time verification of identity. Police may also use a large fingerprint scanner to simultaneously record the fingerprints of all four fingers on each hand, referred to as a “slap.” The purpose of a slap, on a conventional (ink-on-paper) fingerprint card, is to verify that each fingerprint image has been placed in the correct box on the card. When a “slap” is obtained with a scanner, the purpose is the same, i.e., to verify that the correct fingers have been used to obtain of each of four separately scanned fingerprints. A very large and expensive scanning device is used to obtain the “slap.”
It will be apparent from the foregoing that there is a need for alternative technique or improving the accuracy and convenience of fingerprint identity verification systems. The present invention is directed to this end.